The present invention relates to electric meters and, more particularly, to power supplies and power monitors for electronic demand registers of electric meters.
Conventional electric meters employ an aluminum disk driven as a rotor of a small induction motor by an electric field at a speed which is proportional to the electric power being consumed by a load. Geared dials, or cyclometer discs, integrate the disk motion to indicate the total energy consumed, conventionally measured in kilowatt hours (one kilowatt hour equals one thousand watts of power consumption for one hour).
In addition to the above measurement of consumption, some electric meters contain means for separating the consumption into those parts of comsumption occurring during peak and off-peak hours (however defined) and for recording maximum demand during a predetermined period of time in order to adjust billing according to such parameters. In one such demand meter disclosed in U.S. Pat. No. 3,586,974, a mechanical demand register records the power usage during a predetermined period of time and stores the value for reading. The predetermined period of time may be, for example, the time between meter readings, or a period of time corresponding to the billing period of the utility providing the power. A clockwork mechanism restarts the demand register at the ends of regular demand intervals of, for example, a fraction of an hour, so that, at the end of the predetermined period, the stored value represents the highest value of power usage occurring during any one of the regular demand intervals in the predetermined period.
Demand registers of the mechanical type, such as disclosed in the above U.S. patent, have limited flexibility. Once their design is completed for a particular meter physical configuration, the design is not transferrable to a meter having a different physical configuration. In addition, the demand-measurement functions cannot be redefined without major mechanical redesign.
Greater flexibility may be obtainable using electronic acquisition, integration and processing of power usage. An electronic processor such as, for example, a microprocessor may be employed to manage the acquisition, storage, processing and display of the usage and demand data. U.S. Pat. Nos. 4,179,654; 4,197,582; 4,229,795; 4,283,772; 4,301,508; 4,361,872 and 4,368,519, among others, illustrate the flexibility that electronic processing brings to the power and energy usage measurement. Each of these electronic measurement devices includes means for producing an electronic signal having a characteristic such as, for example, a frequency or a pulse repetition rate, which is related to the rate of power usage. The electronic processor is substituted for the mechanical demand register of the prior art to keep track of the power usage during defined periods of time.
An electronic processor of an electronic demand register conventionally employs volatile random access memory for the high speed and low power consumption characteristics offered by such devices. However, several events can occur during normal and emergency conditions which can threaten the integrity of data being recorded for billing purposes in volatile random access memory. If a power outage, by removing power from the processor and the random access memory, were allowed to erase all data stored in random access memory, then the billing data contained in the erased data would be lost. This is, of course, unacceptable. Some means, therefore, appears desirable for storing data in non-volatile memory when a power outage occurs. On the converse, certain normal deviations of the line power, such as, for example, momentary overvoltage, surges, noise and momentary power outages enduring for a very short time period, must be tolerated.